Device-to-device communication is a well-known and widely used component of many existing wireless technologies, including ad hoc and cellular networks. Examples include Bluetooth and several variants of the IEEE 802.11 standards suite such as WiFi Direct. These systems operate in unlicensed spectrum
Recently, device-to-device (D2D) communications as an underlay to cellular networks (mainly LTE) have been proposed as a means to take advantage of the proximity of communicating devices and at the same time to allow devices to operate in a controlled interference environment. Typically, it is suggested that such device-to-device communication shares the same spectrum as the cellular system, for example by reserving some of the cellular uplink resources for device-to-device purposes. In this disclosure, such D2D communication is referred to as D2D communication within a cellular communication system framework. Allocating dedicated spectrum for device-to-device purposes is a less likely alternative as spectrum is a scarce resource and (dynamic) sharing between the D2D services and cellular services is more flexible and provides higher spectrum efficiency.